X-ray tubes can include a target material for production of x-rays in response to impinging electrons from an electron emitter. In a transmission or end anode x-ray tube, the target material can be on an x-ray window. X-rays can be produced in the target material, then emitted out of the x-ray tube through the window. In a side window x-ray tube, x-rays produced on the target can be transmitted through an interior of the x-ray tube to and through a window (physically separate from the target).
There are various advantages to having an ability to use different regions of the target, i.e. allowing the electron beam to impinge on different regions of the target at different times. One advantage is to allow use of a new region of the target when a previously used region has worn out or become too pitted for further use. Another advantage is to allow for different x-ray energy spectra, which can be done by use of different target materials in different target regions. For example, if the target includes a silver region and a gold region, x-rays emitted when the electron beam is directed at the silver region will have a different energy spectra than x-rays emitted when the electron beam is directed at the gold region. Another advantage is to allow for different target thicknesses. A thinner target region can be used when the x-ray tube is operated at lower voltages and a thicker target region can be used when the x-ray tube is operated at higher voltages.
It can be disadvantageous if the electron beam is redirected to different regions of the target. If x-rays are emitted in one direction while using one region of the anode, then emitted in another direction while using another region of the anode, the x-ray user may need to re-collimate and/or realign the x-ray tube with each different use. This need to re-collimate or realign optics can be undesirable.
Information relevant to attempts to address these problems can be found in U.S. Pat. No. 2,298,335, U.S. Pat. No. 2,549,614, U.S. Pat. No. 3,753,020, U.S. Pat. No. 3,900,751, U.S. Pat. No. 5,655,000, U.S. Pat. No. 6,560,315, and U.S. Pat. No. 7,983,394; U.S. Patent Publication Number US 2011/0135066; and Japan Patent Number JP 3,812,165.